How water-mediated hydrogen bonds affect chlorophyll a/b selectivity in Water-Soluble Chlorophyll Protein

The Water-Soluble Chlorophyll Protein (WSCP) of Brassicaceae is a remarkably stable tetrapyrrole- binding protein that, by virtue of its simple design, is an exceptional model to investigate the interactions taking place between pigments and their protein scaffold and how they affect the photophysical properties and the functionality of the complexes. We investigated variants of WSCP from Lepidium virginicum (Lv) and Brassica oleracea (Bo), reconstituted with Chlorophyll (Chl) b, to determine the mechanisms by which the different Chl binding sites control their Chl a/b specificities. A combined Raman and crystallographic investigation has been employed, aimed to characterize in detail the hydrogen-bond network involving the formyl group of Chl b. The study revealed a variable degree of conformational freedom of the hydrogen bond networks among the WSCP variants, and an unexpected mixed presence of hydrogen-bonded and not hydrogen-bonded Chls b in the case of the L91P mutant of Lv WSCP. These findings helped to refine the description of the mechanisms underlying the different Chl a/b specificities of WSCP versions, highlighting the importance of the structural rigidity of the Chl binding site in the vicinity of the Chl b formyl group in granting a strong selectivity to binding sites

Spatial expression of DNA topoisomerase I genes during cell proliferation in Daucus carota

The spatial expression of carrot (Daucus carota L.) top1 genes encoding the two isoforms of the enzyme DNA topoisomerase I (EC 5.99.1.2) was investigated. In situ hybridization analysis performed with a probe recognizing both top1 transcripts provided evidence that in explanted hypocotyls induced to proliferate in vitro by the addition of the growth regulator 2,4-dichlorophenoxyacetic acid (2,4-D), the mRNA accumulation parallels the proliferation of provascular cells of the stelar cylinder. During somatic embryogenesis, the histological distribution of top1 transcripts was strongly evident at the stage of torpedo-shaped embryos, but gene expression was not only restricted to meristematic regions. When the spatial localization was extended to carrot vegetative apices and the investigation was carried out with specific probes for top1a and top1b, both transcripts preferentially accumulated in tissues having mitotic activity

Bulk and surface switching in Mn-Fe-based Prussian Blue Analogues

Many Prussian Blue Analogues are known to show a thermally induced phase transition close to room temperature and a reversible, photo-induced phase transition at low temperatures. This work reports on magnetic measurements, X-ray photoemission and Raman spectroscopy on a particular class of these molecular heterobimetallic systems, specifically on Rb0.81Mn[Fe(CN)6]0.95_1.24H2O, Rb0.97Mn[Fe(CN)6]0.98_1.03H2O and Rb0.70Cu0.22Mn0.78[Fe(CN)6]0.86_2.05H2O, to investigate these transition phenomena both in the bulk of the material and at the sample surface. Results indicate a high degree of charge transfer in the bulk, while a substantially reduced conversion is found at the sample surface, even in case of a near perfect (Rb:Mn:Fe=1:1:1) stoichiometry. Thus, the intrinsic incompleteness of the charge transfer transition in these materials is found to be primarily due to surface reconstruction. Substitution of a large fraction of charge transfer active Mn ions by charge transfer inactive Cu ions leads to a proportional conversion reduction with respect to the maximum conversion that is still stoichiometrically possible and shows the charge transfer capability of metal centers to be quite robust upon inclusion of a neighboring impurity. Additionally, a 532 nm photo-induced metastable state, reminiscent of the high temperature Fe(III)Mn(II) ground state, is found at temperatures 50-100 K. The efficiency of photo-excitation to the metastable state is found to be maximized around 90 K. The photo-induced state is observed to relax to the low temperature Fe(II)Mn(III) ground state at a temperature of approximately 123 K.Comment: 12 pages, 8 figure

Lengthweight relationship and parameters of growth for the checkered puffer Sphoeroides testudineus from a karstic tropical coastal lagoon: La Carbonera, Yucatan, Mexico

Summary This study reports length-weight relationships and growth parameters for Sphoeorides testudineus from La Carbonera, a karstic tropical coastal lagoon on the northwestern coast of the Yucatan Peninsula, Mexico. A total of 461 specimens were collected between April 2009 and March 2010. The lengthweight relationship was W = 0.061Lt 2.98 . Model parameters of the von Bertalanffy growth equation were: L ∞ = 29.50 cm, k = 0.77 year À1 and t 0 = À0.168 years. Introduction Sphoeroides testudineus, a member of the Tetraodontidae family, is known colloquially as checkered puffer and locally as 'xpu' (Mayan) and 'pez globo' (Spanish). It is an important estuarine-dependent fish species of ecological and commercial importance. The checkered puffer is the dominant species in many Yucatan coastal lagoons (Arceo-Carranza and Vega-Cendejas, 2009). The aim of this study was to present the LWR and to estimate the parameters of growth of S. testudineus from La Carbonera lagoon in northwestern Yucatan Peninsula. Materials and methods Samples of S. testudineus were collected during daytime between April 2009 and March 2010 in La Carbonera lagoon, a karstic coastal lagoon in northwestern Yucatan Peninsula, Mexico (21°13′-21°14′N; 89°52′-89°54′W). Collected specimens were euthanized in ice slurry, preserved in formaldehyde (4%) and transported to the laboratory where they were measured (±0.1 mm) and weighed (±0.01 g). The collected fishes were classified under three climatic seasons representing dry (March-June), rainy (July-October), and when there were prevailing north winds (NovemberFebruary). To determine parameters a and b, a regression analysis of log-converted total weight and total length was used. The 95% confidence intervals for b (CI 95%) were calculated to determine if the hypothetical value of isometry (3) fell between these intervals ÀkðtÀt0Þ , where Lt is the length at age t, L ∞ is asymptotic length, k is the growth rate (year À1 ) and t 0 is the hypothetical age of fish at length zero. The growth performance index (u') proposed by Results and discussion From a total of 461 of S. testudineus collected during the study period, 33.8% were collected in the dry season, 30.2% in the rainy season and 36% during the season when north winds prevaile